The invention pertains to light mixer arrangements for providing substantially homogenous light spots. In particular, implementations of document validation subsystems utilizing a light mixer for generating substantially homogenous light spots, and methods of construction are described.
In the field of bill validation, validators used in vending machines and the like typically utilize optical, magnetic and other sensors to obtain data from an inserted bill. In some units, a plurality of light-emitting diode (LED) light sources and phototransistor receivers are positioned on opposite sides of a bill passageway, and generate a plurality of signals corresponding to the light transmitted through the bill as a bill moves past. The signals are processed to determine certain information, such as the position of the bill in the passageway and the authenticity of the bill. The signals are typically compared to predetermined measurements stored in memory that correspond to genuine bills.
Prior art systems utilizing LED light sources also used lenses to focus the light in order to meet system performance requirements. However, some configurations did not provide sufficient light signal levels to accurately validate documents. Further, designs using high power light sources and focusing elements are costly to manufacture.